This invention relates to devices for reading, writing, and storing bit-encoded data, and more particularly to disc drives including packs of multiple, concentrically stacked discs mounted to rotate on stationary spindle shafts.
The continuing effort to increase data storage capacities of magnetic disc drives and other data storage devices is concerned largely with increasing the density at which data can be stored on the available recording surface area. Another approach concerns increasing available recording surface area by mounting multiple discs integrally, concentrically and axially spaced apart from one another on a single spindle assembly. Such spindle assemblies typically include an elongate shaft, a hub that directly supports the discs, and bearing assemblies at opposite ends of the shaft to support the hub and discs for rotation relative to the disc drive frame or housing. Also mounted movably with respect to the housing is an actuator for supporting a plurality of data transducing heads. The actuator, whether of the rotary or linear type, selectively positions the transducing heads relative to the discs.
The spindle shaft can be mounted rotatably to the housing through the bearing assemblies. Alternatively, the shaft is stationary or fixed within the housing, with the hub and discs mounted on the shaft through the bearing assemblies. This latter approach allows a more secure, fixed mounting of the shaft that reduces vibration. The mass and inertia of the rotating parts is reduced, as such parts no longer include the spindle shaft. Further, the stator can be fixed to a stationary PG,4 shaft, eliminating the need for a stationary sleeve or similar part to surround the shaft and support the stator.
Moreover, a stationary spindle shaft provides a conduit for electrical conductors coupled to the stator. More particularly, a central bore is formed in the spindle shaft, open to one end of the shaft and extending axially, i.e. lengthwise along the shaft to a location near the stator. A generally radial aperture extends from the axially inward end of the central bore to the shaft exterior. The flexible cable exits the shaft through the aperture for connection to the stator.
These openings in the spindle shaft give rise to certain difficulties. First, the removal of material to form the openings weakens the spindle shaft. The resonant frequency of the shaft is lower than a solid shaft of identical size and shape, increasing the response time in track-seeking and track-following, and increasing spindle vibration amplitudes in response to actuator movement. The radial aperture introduces an asymmetry which further increases the amplitude and complexity of vibrations introduced in the spindle. These factors limit the efficiency of the disc drive, in terms of extending track-seek times and diminishing transducer positioning accuracy.
Some of these difficulties can be counteracted by providing alternative conduits for electrical conductors. U. S. Pat. No. 4,894,738 (Elsasser et al) discloses a disc drive with a stationary spindle shaft in which a centered, axially extended bore and a generally radial and inclined bore cooperate to provide a conduit, but only for conductors to the stator windings. A separate aperture, formed through a flange or sleeve surrounding one end of the spindle shaft, accommodates conductors associated with commutating and position sensing electronics, as illustrated in FIGS. 5 and 6 of the patent. This arrangement is said to avoid excessive weakening of the shaft. While it does provide for a stronger spindle shaft with a higher resonant frequency, it also raises the need for alternative apertures for electrical conductors, and fails to address the problem of spindle shaft asymmetry.
Therefore, it is an object of the present invention to provide, in a disc drive data storage apparatus, a stationary spindle shaft symmetrical about an axial bisecting plane.
Another object of the invention is to provide a stationary spindle shaft for a disc drive, capable of accommodating conductors for position sensing and commutating as well as conductors to the stator windings, without unduly diminishing the strength or resonant frequency of the shaft.
Yet another object is to provide a stationary spindle shaft in a disc drive, formed with a symmetrical arrangement of radially directed conductor carrying apertures, for enhanced strength and resonant frequency in the shaft to improve the response to vibrations introduced by an actuator of the disc drive during track-seeking and track-following operations.